The present invention relates generally to a device that can be used during an interventional procedure in a stenosed or occluded region of a blood vessel to capture embolic material that might be created and released into the bloodstream as a result of the procedure. The present invention is particularly useful when performing balloon angioplasty, stenting, laser angioplasty, or atherectomy procedures in critical vessels of a patient's body, such as the carotid arteries, where the release of embolic debris into the bloodstream can occlude the flow of oxygenated blood to the brain. The consequences to the patient of such an event are devastating.
A variety of non-surgical interventional procedures have been developed over the years for opening stenosed or occluded blood vessels in a patient caused by the build up of plaque or other substances on the walls of the blood vessel. Such procedures usually involve the percutaneous introduction of the interventional device into the lumen of the artery, usually through a catheter. One widely known and medically accepted procedure is balloon angioplasty in which an inflatable balloon is introduced within the stenosed region of the blood vessel to dilate the occluded vessel. The balloon catheter is initially inserted into the patient's arterial system and is advanced and manipulated into the area of stenosis in the artery. The balloon is inflated to compress the plaque and press the vessel wall radially outward to increase the diameter of the blood vessel.
Another procedure is laser angioplasty which uses a laser to ablate the stenosis by super heating and vaporizing the deposited plaque. Atherectomy is yet another method of treating a stenosed blood vessel in which a rotating cutting blade shaves the deposited plaque from the arterial wall. A vacuum catheter may be used to capture the shaved plaque or thrombus from the blood stream during this procedure.
In another widely practiced procedure, the stenosis can be treated by placing a device known as a stent into the stenosed region to hold open and sometimes expand the diseased segment of blood vessel or other arterial lumen. Stents are particularly useful in the treatment or repair of blood vessels after a stenosis has been compressed by percutaneous transluminal coronary angioplasty (PTCA), percutaneous transluminal angioplasty (PTA), or removal by atherectomy or other means. A stent is usually delivered in a compressed condition to the target site where it is deployed in an expanded condition to support the vessel and to help maintain patency of the lumen.
Prior art stents typically fall into two general categories of construction. The first type of stent is expandable upon application of a controlled force, often through the inflation of the balloon portion of a dilatation catheter that expands the compressed stent to a larger diameter to be left in place within the artery at the target site. The second type of stent is a self-expanding stent formed from, for example, shape memory metals or superelastic nickel-titanum (NiTi) alloys, that self-expands from a compressed state when the stent is advanced out of the distal end of the delivery catheter into the body lumen. The self-expansion of a NiTi stent is triggered either through thermally induced shape memory effect or by the stent's own superelastic properties.
The above non-surgical interventional procedures, when successful, avoid the necessity of major surgical operations. However, there is one common problem associated with all of these non-surgical procedures, namely, the potential release of embolic debris into the bloodstream which can occlude distal vasculature and cause significant health problems to the patient. For example, during deployment of a stent, it is possible that the metal struts of the stent can cut into the stenosis and shear off pieces of plaque, which become embolic debris that travel downstream and lodge somewhere in the patient's vascular system. While not a frequent occurrence, pieces of plaque can sometimes dislodge from the stenosis during a balloon angioplasty procedure and become released into the bloodstream. Additionally, while complete vaporization of plaque is the intended goal during a laser angioplasty procedure, quite often the particles are not fully vaporized and enter the bloodstream. Likewise, emboli created during an atherectomy procedure may enter the bloodstream.
When any of the above-described procedures are performed in the carotid arteries, the release of emboli into the circulatory system can be extremely dangerous and sometimes fatal to the patient. Debris that is carried by the bloodstream to distal vessels of the brain can cause these cerebral vessels to occlude, resulting in a stroke, and in some cases, death. Therefore, although carotid percutaneous transluminal angioplasty has been performed in the past, the number of procedures performed has been limited due to the justifiable fear of causing an embolic stroke should embolic debris enter the bloodstream and block vital downstream blood passages.
Medical devices have been developed to attempt to deal with the problem created when debris or fragments enter the circulatory system following treatment using any one of the above-identified procedures. One approach that has been attempted is cutting the debris into minute sizes which pose little chance of becoming occluded in major vessels within the patient's vasculature. Yet it is often difficult to control the size of the fragments that are formed, and the risk of vessel occlusion still exists.
Other techniques that have been developed to address the problem of removing embolic debris include the use of catheters with a vacuum source that provides temporary suction to remove embolic debris from the bloodstream. On the other hand, complications exist with such systems because the vacuum catheter may not remove all of the embolic material from the bloodstream, and a more powerful suction could cause problems to the patient's vasculature.
Still other techniques that have had success include the placement of a filter assembly downstream from the treatment site to capture embolic debris before it reaches the smaller blood vessels downstream. The filter assembly is typically attached to the distal end of an elongated shaft or guide wire and is delivered to the deployment site via a delivery catheter. Such filters have proven successful in capturing embolic debris released into the bloodstream during treatment. Nevertheless, some filter assembly designs are difficult and/or time consuming to manufacture.
Some existing embolic protection filters include a filter membrane and a basket or cage that supports the filter membrane. The basket can be fabricated from a longitudinal, small diameter hypotube by cutting a particular pattern into the hypotube thus forming the struts, ribs, or framework of the basket. The hypotube can be set to a particular expanded size using successive heat treatments. The heat treatments also relieve stress that can build up in the strut pattern particularly at locations where two or more struts or ribs are joined. Without the heat treatments, the basket can fracture because of the buildup of stress at that joint or at other key areas. Unfortunately, the successive heat treatments add to the cost of manufacturing the baskets. Moreover, the existing baskets may still have low fatigue resistance during use even after being subjected to multiple heat treatments.
What has been needed is a basket for an embolic protection device that is not prone to fracturing during manufacture or use, thereby reducing the need for heat treatment and improving fatigue resistance over conventional filter baskets. The present invention disclosed herein satisfies these and other needs.